This invention relates to an optical disk device, such as optical video disk, optical audio disk, etc., which is used for an information recording device, such as data file. To be more precise, this invention relates to an optical disk production or cutting apparatus for forming optically pregroove tracks on a disk and to an optical disk recording apparatus for recording optically information on the disk.
When data information is recorded by means of an optical disk recording apparatus for data file optical disk, optical video disk file, etc., the data information should be recorded on a disk with a density so high that the track pitch is e.g. 1.6.+-.0.1 .mu.m and with a high precision.
To this end a recording and playing system, by which data information is recorded on a pregrooved disk, has been already proposed (Japanese Patent Application Laid-open No. 49-113601). FIG. 1 shows principal parts of a prior art apparatus for fabricating pregrooved disks.
Pregrooved information is made on a disk by modulating a laser beam emitted by a laser device 1, e.g. argon laser, helium-cadmium laser, by means of an optical modulator 2 and by forming a small light spot 5 on the surface of the rotating disk 6 by means of an objective lens 4. On the disk 6 is applied a layer of photosensitive material 7, e.g. photoresist, and the disk is rotated by a motor 8.
The laser beam is so intensity-modulated by the optical modulator 2 that the sector part is optically 1/4 wavelength deep and the data part is optically 1/8 wavelength deep is a pregrooved track. The pregroove is formed to be spiral. In order to form a spiral pregroove track on the whole surface of the disk 6, an optical system 3 is advanced continuously with a uniform velocity in a radial direction of the disk by a screw. For forming the pregroove track with a track pitch precision of 1.6.+-.0.1 .mu.m on the disk, ultrahigh precision tools, such as an ultrahigh precision lap screw 10, a pneumatic bearing sliding shaft 11, a precision rotary motor 12, an ultrahigh lap gear 13, etc. are used in the mechanism part 9 for advancing the optical system 3. However, it is impossible to keep track pitch errors under 0.1 .mu.m.
FIG. 2A shows an example of positional relations between pregroove tracks 15-1, 15-2 and a recording light spot 17 in the case where data information is recorded on the pregroove track produced by means of the prior art apparatus shown in FIG. 1.
The pregroove tracks 15-1, 15-2 are optically 1/8 wavelength deep and diffracted light of the spot 17 from the center of the track 15-1 can be detected by measuring light reflected by the track by means of a differential light detector (Japanese Patent Application Laid-open No. 54-154304). However, this tracking system is very sensitive to the form of the pregroove and skew of the disk, and it is difficult to record data information with a high reliability on the pregroove tracks 15-1, 15-2, . . .
FIG. 2B shows another example of positional relations between the pregroove tracks 15-1, 15-2 and light spots 17, 18, 19. In the figure the pitch of the pregroove tracks 15-1, 15-2 is 1.6.+-.0.1 .mu.m. The light spot 17 represents the main beam for recording data information and the light spots 18, 19 indicate side beams for tracking. These twin spots 18, 19 are arranged to be on the edges of one pregroove track 15-1 and tracking signals are derived by detecting reflected light from each of the light spots (Japanese Patent Application Publication No. 53-13123).
In the arrangement shown in FIG. 2B, when data 20 information is recorded on the pregroove track 15-1 by using the main beam 17, the side spot 19 for the tracking is not influenced by the data pit 20, but the side spot 18 is influenced by the data pit 20, which gives rise to unbalance in output signals coming from the light spots 18 and 19. As the results tracking can be effected no more precisely.